Synthesis and magnetic properties of centennialite: a new S=1/2 Kagome antiferromagnet and comparison with herbertsmithite and kapellasite

Minerals of the atacamite group such as herbertsmithite and kapellasite have recently attracted enormous attention as the S = A1/2 Kagom, antiferromagnets for achieving the quantum spin liquid (QSL) state with diverse technological applications. Herein we report on the synthesis of the newly discovered mineral centennialite by using an unconventional solid-state reaction method at 463 K. Synthetic centennialite, Ca1.06Cu2.94Cl2.01(OH)(5.99)center dot 0.73H(2)O, has been characterized by scanning electron microscopy, electron microprobe analyses, Fourier-transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analyses, single-crystal X-ray diffraction structure refinements, and magnetic susceptibility measurements. The crystal structure of centennialite is characterized by a perfect (threefold symmetry) Kagom, layer with < 5 % substitution between Ca and Cu and therefore differs from those of herbertsmithite and kapellasite, in which 15-25 % mixing between similar Zn and Cu atoms dramatically affects the QSL state. Centennialite remains antiferromagnetic down to similar to 7 K with a moderate spin frustration (i.e., a Weiss temperature theta = -56 K and a spin frustration parameter f = 8), but exhibits a canted antiferromagnetic ordering with a ferromagnetic component at lower temperatures.